Basic components of modern conventional plasma arc torches include a torch body, an electrode (e.g., cathode) mounted within the body, a nozzle (e.g., anode) with a central orifice that can produce a pilot arc to the electrode to initiate a plasma arc in a flow of a suitable gas (e.g. air, nitrogen or oxygen) and associated electrical connections and passages for cooling, and arc control fluids. Generation of the pilot arc may be by means of a high frequency, high voltage signal coupled to a DC power supply and the plasma arc torch, or any of a variety of contact starting methods. In some configurations, a shield is mounted to the torch body to prevent metal that is spattered from the workpiece (sometimes referred to as slag) during processing from accumulating on torch parts (e.g., the nozzle or the electrode). Generally, the shield includes a shield exit portion (also called a shield orifice) that permits the plasma jet to pass therethrough. The shield can be mounted co-axially with respect to the nozzle such that the plasma exit portion is aligned with the shield exit portion.
Cooling capacity has been a limitation of previous designs relating to plasma arc torches. For example, previous designs have required the use of cooling mediums other than or in addition to a gas (e.g., cooling water or liquid) for torches that operate at high (e.g., 100 or 200 Amps, or more) current levels. Most of these cooling methods can require cooling systems external to the torch (e.g., which can include water supplies, reservoirs, heat exchange equipment, supply pumps, etc.). External cooling systems can increase the associated equipment expense, can require more maintenance, be vulnerable to spills, and in some cases, can require disposal of the cooling medium. The issue of cooling the plasma arc torch is more acute for higher current systems, as higher current systems can generate more heat and have larger cooling demands. Indeed, commercially available plasma arc torch cutting systems operating at more than about 100 amperes typically utilize cooling systems using a liquid coolant (e.g., water or glycol). However, other systems are possible.